Visitor ( but curriki member) having Start button for adding Xwiki page.Saving that pgae throws Error.

Login as a user who is a Curriki member but visitor of a group- Visit an open group.
It is noted that even if he is not a member of this group, Start button and upload button is shown for this visitor.
If he clicks the Start button and enter some data in the Xwiki page and click Save, an Error message is thrown.